Flash player doesn't work/not showing up in Plugins tab

Hello! I'm trying to get the flash player working in Vivaldi, but I have no idea how, so I hope you guys can help me out! I installed the Flash Player normally, like, I downloaded it from Adobe and ran the installer several times, I even reinstalled it and it still doesn't show up in the Plugins tab? Is there a way to fix this, or to make Flash work with Vivaldi? Even though most websites nowadays use HTML5, there's still some forums that use embedded video links which show up as flash. Hope you guys can help me out!